如何按组选择最大值和最大值计数

Question

我有一张桌子，我必须在其中按姓名和性别计算最大值和（计算最大值）组的数量。

sample input:  

name sex age  
 A    F  2  
 A    F  3  
 A    M  4  
 B    F  6  
 B    M  7  
 B    M  7  
 B    F  4  
 C    M  8  
 C    M  8  
 C    M  8  
 C    M  3  
 C    F  1  
 C    F 10  
 C    F 10  

Sample Output:  
name    sex max_age count_max_age
A        F        3          1
A        M        4          1
B        F        6          1
B        M        7          2
C        F       10          2
C        M        8          3

我尝试过

select name,sex,max(age) as max_age , count(max_age) from table_1 group by name ,sex  

我遇到错误

Unknown column max_age in fieldlist

请提出以上查询所需的任何修改。
预先感谢

Answer 1

SELECT count(max_age), name, sex FROM (
  SELECT name, sex, max(age) as max_age from table_1 group by name, sex
) as max_age_group group by name, sex

查询不会在同一级别理解别名，但是您可以将其作为子查询。

Answer 2

使用子查询并按如下所示加入

select 
    t1.name, t1.sex, max_age, count(max_age) as countofmaxage 
from 
    (select name, sex, max(age) as max_age 
     from t 
     group by name, sex) t1 
join 
    t on t1.name = t.name and t1.sex = t.sex and t1.max_age = t.age
group by 
    t1.name, t1.sex, max_age

输出：

name    sex max_age countofmaxage
----------------------------------
A        F     3            1
A        M     4            1
B        F     6            1
B        M     7            2
C        F     10           2
C        M     8            3

DEMO in fiddle